The overall goal is to investigate the effects of hypothermia and the innervation of the heart on cardiac muscle cells. We propose to study cardiac tissues from the bat in active and hibernating stages and to evaluate quantitatively and systematically the dynamics of the transition which occurs during the period of arousal, a time of temperature change and intense sympathetic neural activity. This evaluation will include an ultrastructural morphometric analysis of myocardial organelles, continued investigation of the role of endogenous norepinephrine, and cytochemistry. The morphological information will be correlated with measurements of the endogenous norepinephrine content and radioisotopic measurements of norepinephrine turnover. Norepinephrine-related studies will include an investigation of the effect of alpha and beta adrenergic blocking drugs on the phenomenom of lipid droplet accumulation during arousal as well as the action of these drugs on agents such as isoproterenol and norepinephrine itself, which induce myocardial necrosis. In addition, the action of 6-hydroxydopamine and atropine on the effect of arousal on the heart will be investigated further. A study of possible cyclic AMP-norepinephrine interrelationships during arousal will be undertaken. Also, cytochemistry will be done at the level of electron microscopy in order to determine the sites of localization of cholinesterase and adenosine triphosphatase as well as seasonal and functional variation in their activity. Lastly, a scanning electron microscopic study of the interior surface of the bat heart during arousal from hibernation will be carried out.